16  Unit 4: Earth-Sun Dynamics 5E

What factors have contributed to climate change in the past and are they contributing to climate change now?

Author

Earth & Space Science

HS-ESS2-4

17 Investigative Phenomenon

17.1 🔬 Phenomenon

The amount of radiation received at 65°N has gone up and down over the last 750,000 years and repeats a pattern about every 100,000 years.

17.1.1 Driving Questions:

  • How does the Sun contribute to climate change?
  • What was the planet’s orbit like in the past and what is it like now?
  • Has the Earth always had the same tilt, or does it change?
  • Can these factors explain climate change in the past?
  • What’s their impact on the current climate?

18 Engage: Temperature Patterns Over 400,000 Years

18.1 Ice Core Temperature Record

Let’s examine temperature data from Antarctic ice cores spanning 400,000 years.

18.1.1 ✅ Initial Observations

  1. What pattern do you notice in the temperature data?
  2. Approximately how often do the warm periods (interglacials) occur?
  3. What might be causing these regular cycles?

19 Explore: Milankovitch Cycles

19.1 The Three Orbital Cycles

Serbian scientist Milutin Milankovitch proposed that variations in Earth’s orbit cause long-term climate cycles. Let’s explore each one.

19.1.1 Cycle 1: Eccentricity (~100,000 year cycle)

Earth’s orbit changes shape from nearly circular to more elliptical.

19.1.2 Cycle 2: Obliquity (Axial Tilt) (~41,000 year cycle)

Earth’s axial tilt varies between 22.1° and 24.5°.

19.1.3 Cycle 3: Precession (~23,000 year cycle)

Earth’s axis wobbles like a spinning top, changing which hemisphere is tilted toward the Sun at perihelion.

19.2 🔬 Lab Activity: Milankovitch Cycle Investigation

19.2.1 Materials Needed:

  • Graph paper or spreadsheet
  • Colored pencils
  • Calculator

19.2.2 Procedure:

Part 1: Analyzing the Cycles

  1. Use the interactive simulations above to explore each cycle
  2. Record observations in your data table:
Cycle Period Current Value Range Climate Effect
Eccentricity ~100,000 yrs 0.017 0.0 - 0.06 Changes total radiation received
Obliquity ~41,000 yrs 23.5° 22.1° - 24.5° Changes seasonal contrast
Precession ~23,000 yrs N/A 360° rotation Changes timing of seasons

Part 2: Combining the Cycles

The graph below shows how these cycles combine to affect radiation at 65°N:

Part 3: Correlation Analysis

Compare the radiation graph above with the temperature graph from the Engage section. Answer:

  1. Do high radiation periods correlate with warm periods (interglacials)?
  2. What is the approximate lag time between radiation changes and temperature changes?
  3. Why might there be a delay in temperature response?

20 Explain: How Milankovitch Cycles Drive Ice Ages

20.1 🌍 The Mechanism

Key Insight: It’s not total yearly radiation that matters most—it’s summer radiation at high northern latitudes (around 65°N).

20.1.1 Why 65°N Matters:

  1. Most of Earth’s land mass is in the Northern Hemisphere
  2. Ice sheets grow when summer is NOT warm enough to melt winter snow
  3. When summer radiation at 65°N is LOW, ice sheets expand
  4. When summer radiation at 65°N is HIGH, ice sheets retreat

20.1.2 The Feedback Loop:

Low summer radiation → Snow persists → Ice sheets grow → 
Higher albedo → More cooling → More ice growth

20.2 Comparing Radiation and Temperature

20.2.1 💡 Key Ideas: Earth-Sun Dynamics

  1. Temperatures on Earth have fluctuated greatly during human history, marked by glacial and interglacial periods
  2. A pattern exists in the frequency of these fluctuations (~100,000 years)
  3. The pattern is explained by cyclical changes in Earth’s orbit shape and tilt
  4. These changes cause ice sheets to expand and retreat
  5. Current orbital parameters suggest Earth should be cooling, yet global temperatures are increasing

21 Elaborate: What About the Sun’s Output?

21.1 Solar Radiation Data

Some claim changes in the Sun’s output are causing current warming. Let’s examine the evidence:

21.1.1 ✅ Analysis Questions

  1. Has solar output increased significantly since 1980?
  2. Has temperature increased significantly since 1980?
  3. Can changes in solar output explain recent warming? Why or why not?

22 Evaluate: Current Orbital Position

22.1 📊 Putting It Together

Based on current orbital parameters:

Parameter Current Value Trend Climate Effect
Eccentricity 0.017 Decreasing Less seasonal variation
Obliquity 23.44° Decreasing Less extreme seasons
Precession NH summer at aphelion Changing slowly Cooler NH summers

Conclusion: Based on Milankovitch cycles alone, Earth should be gradually cooling. The fact that Earth is warming despite this indicates another factor is at play.

This sets up our next investigation: What IS causing the warming?

22.2 📝 Earth-Sun Dynamics Quiz

Question 1: What is the approximate period of the eccentricity cycle? - A) 23,000 years - B) 41,000 years - C) 100,000 years - D) 1 million years

Question 2: Why is summer radiation at 65°N latitude so important for ice ages? - A) It’s where most people live - B) It’s where most land mass is located, and ice sheets need cool summers to persist - C) The Sun is closest to Earth at this latitude - D) Ocean currents are strongest here

Question 3: Earth’s current axial tilt is approximately: - A) 22.1° - B) 23.5° - C) 24.5° - D) 45°

Question 4: According to Milankovitch cycles, what should Earth’s climate be doing right now? - A) Warming rapidly - B) Staying constant - C) Cooling gradually - D) Experiencing an ice age

Question 5: What causes the ~100,000 year glacial-interglacial cycle? - A) Changes in the Sun’s energy output - B) Volcanic activity - C) Changes in Earth’s orbital eccentricity - D) Human activity

Question 6: The precession cycle affects climate by: - A) Changing total solar radiation received - B) Changing which season occurs at perihelion vs aphelion - C) Changing Earth’s distance from the Sun - D) Changing the Sun’s output

Question 7: If Earth’s axial tilt increased to 24.5°, seasons would become: - A) Less extreme - B) More extreme - C) Unchanged - D) Reversed

Question 8: What is the significance of global warming occurring despite Milankovitch cycles predicting cooling? - A) Milankovitch cycles are wrong - B) Another factor must be causing the warming - C) The Sun’s output has increased dramatically - D) Earth’s orbit has changed unexpectedly

Answers: 1-C, 2-B, 3-B, 4-C, 5-C, 6-B, 7-B, 8-B